Normalized Testosterone Glucuronide as a Potential Urinary Biomarker for Highly Variable UGT2B17 in Children 7-18 Years

Abstract

UDP-glucuronosyltransferase 2B17 (UGT2B17) is a highly variable androgen-metabolizing and drug-metabolizing enzyme. UGT2B17 exhibits a unique ontogeny profile characterized by a dramatic increase in hepatic protein expression from prepubertal age to adulthood. Age, sex, copy number variation (CNV), and single nucleotide polymorphisms only explain 26% of variability in protein expression, highlighting the need for a phenotypic biomarker for predicting interindividual variability in glucuronidation of UGT2B17 substrates. Here, we propose testosterone glucuronide (TG) normalized by androsterone glucuronide (TG/AG) as a urinary UGT2B17 biomarker, and examine the associations among urinary TG/AG and age, sex, and CNV. We performed targeted metabolomics of 12 androgen conjugates with liquid-chromatography tandem mass spectrometry in 63 pediatric subjects ages 7-18 years followed over 7 visits in 3 years. Consistent with the reported developmental trajectory of UGT2B17 protein expression, urinary TG/AG is significantly associated with age, sex, and CNV. In conclusion, TG/AG shows promise as a phenotypic urinary UGT2B17 biomarker.

Figure 1.. Androgen metabolism scheme.

Simplified androgen metabolism scheme^, is shown, with relative UGT contribution in glucuronidation depicted in blue. Dashed arrow and box indicate a separately regulated metabolic pathway for epitestosterone and epiandrosterone that is not fully understood.

Figure 2.. TG, AG, and TG/AG with age and CNV, by sex.

Testosterone glucuronide (TG), androsterone glucuronide (AG), and TG/AG with age is shown in A, B, and C, and TG and AG with copy number variation (CNV) is shown in D and E, respectively. TG/AG with CNV is separated by sexual maturity rating (SMR) at stage 1 (F) and stages 4 and 5 (G), to remove the influence of sexual maturation. Males are depicted in blue triangles and females in pink circles; line and bars show median and interquartile ranges.

Figure 3.. Association of urinary TG/AG levels with age, sex, race, and CNV.

Model-fitted log (TG/AG) with age splines set at 11 and 14 years is shown with males in blue and females in pink (A). Log (TG/AG) association with race is shown in B, with African Americans (AA) in dark brown and Caucasian Americans (CA) in light brown. Log (TG/AG) association with copy number variation (CNV=0 in light grey, CNV=1 in dark grey, CNV=2 in black) is shown for males (C) and females (D).